I want to second this suggestion. With some good advertising and some bad math you could probably convince some users that they're practically guaranteed(!) to earn money from one of the lottery's run whenever there data is sold. Tie that to some instand credit card (paypal account?) and you could also track what they choose to buy with their winnings.

Does anyone remember the name of that new credit card company that is sopposed to be competing with paypal and Google Checkout?